A number of different structures are known for use in molecular separations. The size of the pores of the structure defines the upper limit of the dimensions of the molecules that can pass through it. For example, zeolites and microporous silica membranes have pore sizes of up to 9 angstroms. Mesoporous membranes have pore sizes which are 20 angstroms and larger. This leaves a gap between pore sizes of 9 and 20 angstroms which is not addressed sufficiently by current technology. Many important organic and biological molecules fall into this size range. The paucity of synthetic methods available for creating suitable structures having pore sizes within this range has limited the use of these structures in the separation of such molecules.